Rock drill with socket having a curved surface



E. G. EELES 3,213,951

ROCK DRILL WITH SOCKET HAVING A CURVED SURFACE Oct. 26, 1965 Filed May16, 1963 PA'FIB \"I' AGE NT United States Patent Cfifice 3,213,951Patent ed Oct. 26, 1965 Surveys Filed May 16, 1963, Ser. No. 280,860 11Claims. (Cl. 175-414) This invention relates to rock drill bits anddrilling assemblies and other structures where transmission of a forcethrough a demountable joint is required.

A conventional push-on type of drill bit comprises a cutting head and arod-receiving socket portion having a skirt with an interior linearlytapered surface section and usually a second surface section ofapproximately constant diameter, and a dome. The rod for use with such abit has a linearly tapered end section of complementary dimensions forengagement with the tapered surface section of the bit skirt. Theseconventional bits have a limited life due to operational failures whichmost frequently are radial fractures in the skirt (ring-offs) and, to alesser extent, radial failures through the base of the dome and theWater hole in the cutting head.

It has been determined that the use of linear tapers results in a largehoop stress discontinuity with resulting tensile forces which causefatigue failures in the conventional bits.

It is an object of this invention to provide a drill bit and rodassembly which will result in reduced hoop stress discontinuity withconsequent less failure incidence and increased operational life.

The invention will be described with reference to the accompanyingdrawing, the single figure of which is a sectional elevation of a bitand rod assembly in accordance with the invention.

Referring to the drawing, 10 is a drill rod and 11 a bit in accordancewith the invention.

The bit 11 has a cutting head 12 with Water holes 13 and a skirt 14having an interior cylindrical surface 14a forming a socket 15 forreception of the tapered end 16 of the rod 10.

In accordance with the invention, the interior or rodseating surfaceportion 17 of the bit skirt is of a curved tapered contour, and thecomplementary surface 18 of the rod end 16 is of a nearly mating curvedtapered contour.

of the skirt leading to the dome 21 in order that there be no abruptchange in hoop stress at the root.

It will be apparent that the entire cylindrical surface 14a of the skirt14 and comprising the surfaces 17 and 19 and dome 21, constitutes theentire longitudinal extent of the socket. The interior cylindricalsurface 14a of the skirt is fundamentally circular in cross-sectionthroughout its extent and has a longitudinal axis of symmetry. Aspreviously indicated, the surface portion 17 is curved in thelongitudinal section thereof. The surface 14a has a maximum diameter ofsuccessively decreasing degree from the mouth throughout the entirelongitudinal extent of such surface.

It will be apparent that the provision of such surfaces 17 and 18 on thebit and rod makes possible an arrangement of such surfaces whereby truetangential separation of rod and bit is possible. It will be recognizedthat the provision of a theoretically-ideal rod shape is impractical,since it would be confined to one specific load for each shape, and theconfiguration chosen must be tolerant of production variables. However,there is illustrated in the figure the geometry of one configuration Itis quite desirable that, as shown, there be a: smooth tangentialtransition of the surface portion 17 to the surface portion 19 of theconstant diameter section 20 using nearly mating radii which issatisfactory for practic511 purposes and which approximates most closelyto the l 63 I It is emphasized that there are many other geometricalconfigurations that are satisfactory, including one with nearly matingsurfaces of opposite signs to those illustrated and nearly matingsurfaces of non-constant radii of both signs. A concave radius on therod and a convex radius on the bit are defined as those illustrated inthe figure.

In the drawing,

F is a plane lying normal to the longitudinal axis of the bit and inwhich lies the socket mouth end of the bit.

L is a plane lying normal to the longitudinal axis of the bitdeirad inwhich occurs the juncture of surfaces 17 an AC =R=radius of rod surface18. AO=r -radius of bit surface 17. BE=x=root clearance.

FL: =length of tapered section of bit. D=diameter of mouth.

d=diameter of surface 19.

a=mouth angle.

. It will be apparent that, if the radii AC and A0 were identical, theroot clearance BE would be zero. This arrangement would of course beimpractical since it is intolerant of production variables.

Considering triangle AOC,

It will be observed that the mouth angle on equal 20.

The following table gives by way of example suitable dimensionalcharacteristics of curved taper bits in accordance with the invention,based upon a mouth diameter (D) of 0.875 inch.

TABLE I Examples of dimensions for curved taper bits 7 1 (in) r (in.) ad (in) 1. 4. 0 3240 O. 549 1.125 5. 0 26 0.619 1. 125 6. 0 2136 0.663 1. 25 5. 0 2858 0. 557 1. 25 6.0 241 0.611 1. 25 7. 0 2034 0. 649 1.25 8. 0 1758 0. 679 1. 375 5. 0 3156 0. 489 1. 375 6. 0 2630 0. 555 1.375 7. 0 2240 0. 603 1. 375 8. 0 1948 0 637 1. 375 9. 0 1734 0. 667 1.50 6. 0 2858 0. 493 l. 50 7. 0 2446 O. 549 1. 50 8. 0 2136 0. 591 1. 509. 0 1912 0. 623 1. 50 10. 0 1716 0. 649

In one form of standard bit, the taper length (y) is 1.25 inches with avalue for d of 0.65 inch. It is not desirable to use values of dsignificantly above this figure, as the consequent reduction of sectionmay result in failures on a pseudo-buckling basis. The value of d cannotbe reduced excessively, as the necessary resultant reduction in rod tipdiameter may be impossible on some, rods due to non-axiality of thewater hole. The choice of dimensions giving a high mouth angle (a) isnot desirable, as the interference forces holding the bit onto the rodtraction of the clearance from the values of at given in I Table I.

TABLE 2 Examples of values of rod radius and root diameter for mostsuitable clearances and bit dimensions Taper Bit Root Rod Rod Root 1Length Radius Clearance Radius Diameter 11 3- a at 037 5 125 0. 0090 5.50 0432 0. 0218 5. 00 0194 2a 0. 0 34 25 0 0. 0033 0. 50 0314 0. 0191 0.00 .0103 0. 0013 7. 00 0704 0. 0021 7. s0 0733 25 0 0. 0000 7. 50 00330. 0143 7. 00 0504 0. 0020 0. 90 32 0.0041 6.80 .5 375 O 0. 0107 0. 505816 0. 0233 0. 00 5504 0. 00 5 7. 0 224g 0. 00 1 7.3 0 1-375 M 0 00317. 00 .0203 0. 0173 7. 00 0043 3;" 2-3 223 0. 24 375 0 0. 0003 s. 500544 0. 0134 s. 00 0402 0. 0013 7. 00 5874 1 5 8 0 0.0037 7.30 .5330 0.0007 7. 50 5710 0. 0207 7. 00 5490 0. 0014 3. 00 0202 1 5 9 0 0.00298.80 .0172 0. 0075 s. 50 0030 0. 0100 s. 00 5010 0. 0012 9. go 2122 0.0023 0. 0 5 0 0. 0000 9. 50 0370 0. 0127 9. 00 .0230

Due to the curved nature of the contact between rod and bit, the use ofthe usual brass shim is rather impractical, but zinc spraying of thecontacting surface of the bit may be used provided suitable dimensionalchanges are made in the bit and/or rod to compensate.

It should be observed that in the case considered the radius centre ofthe rod is in line with the end of the rod, while that of the bit is ata distance from the open end equal to the length of the taper section.

The data given in the tables is given by way of example for oneconfiguration for one specific drill size; similar data for other sizescan readily be computed using the relations given.

As given in Table 2, the taper length is 1.125 to 1.50 inches, the bitradius 6 to 10 inches and the root clearance 0.010 to 0.050 inch.

The expression root clearance as employed in the appended claims meansthe radial clearance between the mating surfaces of rod and bit in theassembly at the root or small diameter section of such surfaces.

While the foregoing description has been directed mainly to drillingassemblies, it will be understood that the basic principals involved areequally applicable to any other structure involving the transmission ofa force through'a demountable joint.

I claim:

1. A drilling device comprising a drill bit having a cutting head and arod receiving skirt defining a socket, said skirt having an interiorcylindrical surface constituting the entire longitudinal extent of saidsocket and an edge defining the mouth of said socket, said surface beingfundamentally circular in cross-section throughout its extent and havinga longitudinal axis of symmetry, said surface being curved in thelongitudinal section thereof and having a maximum diameter at said mouthand a diameter of successively decreasing degree from said mouththroughout the entire longitudinal extent of said surface.

2. A drill bit as defined in claim 1, said curved surface being convex.

3. A drill bit as defined in claim 1, said curved surface being ofconstant radius.

4. A drill bit comprising a cutting head and a skirt defining a socket,said skirt having an interior cylindrical surface constituting theentire longitudinal extent of said socket and an edge defining the mouthof said socket, said surface having a longitudinal axis of symmetry andbeing circular in cross-section throughout its extent, said surfacehaving a constant diameter portion remote from said mouth and a secondportion extending from said constant diameter portion to said mouth,said second portion being curved in the longitudinal section thereof ona radius the center of which lies in a plane normal to said longitudinalaxis and in which occurs the juncture of said surface portions, saidsurface having a maximum diameter at said mouth and a diameter ofsuccessively decreasing degree from said mouth throughout the entirelongitudinal extent of said surface.

5. A drill bit as defined in claim 4, the length of said curved surfacebeing 1.125 to 1.50 inches, and said radius of curvature being 6 to 10inches.

6. A drill bit as defined in claim 5, said curved surface having adaimeter of about 0.549 to 0.679 inch. v

7. A drilling assembly comprising a drill bit having a cutting head anda skirt defining a socket, said skirt having an interior cylindricalsurface constituting the entire longitudinal extent of said socket andan edge defining the mouth of said socket, said surface having alongitudinal axis of symmetry and being circular in cross-sectionthroughout its extent, said surface having a constant diameter portionremote from said mouth and a second portion extending from said constantdiameter portion to said mouth, said second portion being curved in thelongitudinal section thereof on a radius the center of which lies in aplane normal to said longitudinal axis and in which occurs the junctureof said surface portions, said surface having a maximum diameter at saidmouth and a diameter of successively decreasing degree from said mouththroughout the entire longitudinal extent of said surface, and a rodhaving an end portion the surface of which is curved in the longitudinalsection thereof on a constant radius, said rod surface being ofgradually decreasing diameter towards the adjoining end of said rod, thediameter range of said second surface portion of said socket beingapproximately the same as that of said rod end portion surface.

8. A drilling assembly as defined in claim 7, the center said radius ofcurvature of said rod end portion surface lying in the diametral planeof said adjoining end of said rod, said curved surface of said sockethaving a ;oot clearance with respect to said rod end portion surace.

9. A drilling assembly as defined in claim 8, said root clearance beingin accordance with the formula 7 Sin 0. tan r(1Cos 6) where r is saidradius of curvature of said bit surface section, 0 is the angle of rwith said plane of juncture, and 1 is the angle of said radius ofcurvature of said rod surface with said diametral plane.

10. A drill bit comprising a cutting head and a rodreceiving skirthaving a rod-engageable interior surface, said surface having a domesection constituting the inner end thereof, and an outer end defined bythe edge of said skirt, said surface being circular in cross-sectionthroughout its extent and having a longitudinal axis of symmetry, theportion of said surface adjoining said dome section being of constantdiameter, and the remaining portion of said surface being curved in thelongitudinal section thereof, and having a gradually increasing diameterfrom a minimum diameter at the juncture With said constant diameterportion to a maximum diameter at said outer end.

11, A joint assembly comprising a first member having a skirt defining asocket, said skirt having an interior cylindrical surface constitutingthe entire longitudinal extent of said socket and an edge defining themouth of said socket, said surface having a longitudinal axis ofsymmetry and being circular in cross-section throughout its extent, saidsurface having a constant diameter portion remote from said mouth and asecond portion extending from said constant diameter portion to saidmouth, said second portion being curved in the longitudinal sectionthereof on a radius the center of which lies in a plane normal to saidlongitudinal axis and in which occurs the juncture of said surfaceportions, said surface having a maximum diameter at said mouth and adiameter of suc cessively decreasing degree from said mouth throughoutthe entire longitudinal extent of said surface, and a second ReferencesCited by the Examiner UNITED STATES PATENTS 1,203,025 10/ 16 McClain30633 2,131,056 9/38 Lind 279-103 2,354,656 8/44 Annesley 287-l262,421,826 6/47 Baker 287-126 2,967,738 1/61 Moore 30633 3,027,953 4/62Coski 175409 BENJAMIN HERSH, Primary Examiner.

20 CARL W. TOMLIN, Examiner.

1. A DRILLING DEVICE COMPRISING A DRILL BIT HAVING A CUTTING HED AND AROD RECEIVING SKIRT DEFINING A SOCKET, SAID SKIRT HAVING AN INTERIORCYLINDRICAL SURFACE CONSTITUTING THE ENTIRE LONGITUDINAL EXTENT OF SAIDSOCKET AND AN EDGE DEFINING THE MOUTH OF SAID SOCKET, SAID SURFACE BEINGFUNDAMENTALLY CIRCULAR IN CROSS-SECTION THROUGHOUT ITS EXTENT AND HAVINGA LONGITUDINAL AXIS OF SYMMETRY, SAID SURFACE BEING CURVED IN THELONGITUDINAL SECTION THEREOF AND HAVING A MIXIMUM DIAMETER AT SAID MOUTHAND A DIAMETER OF SUCCESSIVELY DECREASING DEGREE FROM SAID MOUTHTHROUGHOUT THE ENTIRE LONGITUDINAL EXTENT OF SAISD SURFACE.